1. Field of the Invention
The present invention relates to a tandem pump apparatus wherein a first hydraulic pump for supplying operating fluid to a first actuator and a second hydraulic pump for supplying operating fluid to a second actuator work in cooperation with each other.
2. Description of the Related Art
A tandem pump apparatus of the aforementioned type is disclosed in, for example, Japanese Patent Laid-Open No. Sho 62-139918, wherein a first hydraulic pump is provided with a first flow rate control valve for refluxing a surplus of the flow discharged from the first hydraulic pump to a suction side of the pump through a first relief passage, and a second hydraulic pump is provided with a second flow rate control valve for refluxing a surplus of the flow discharged from the second hydraulic pump to a suction side of the pump through a second relief passage, so that the supercharging effect by the refluxes will restrain cavitation in the hydraulic pumps.
There normally is a flow rate difference between the flow rate of the reflux to the suction side of the first hydraulic pump through the first relief passage and the flow rate of the reflux to the suction side of the second hydraulic pump through the second relief passage (the flow rate difference is normally determined to a specific value if the first actuator and the second actuator are specified). Such different flow rates result in different cavitation restraining effects achieved by the supercharges into the two hydraulic pumps.